Device and method for serial data transmission between a position-measuring device and a control unit

ABSTRACT

In a device and a method for serial data transmission between a position-measuring device and a control unit, made up of an interface unit on the control side and an interface unit on the measuring-device side, which are connected to each other for the transmission of serial data packets with the aid of a bidirectional data channel, the interface unit on the control side includes a control-side transmitter unit for transmitting serial data packets via the data channel to a measuring-device-side receiver unit disposed in the interface unit on the measuring-device side. The interface unit on the measuring-device side includes a measuring-device-side transmitter unit for transmitting serial data packets via the data channel to a control-side receiver unit disposed in the interface unit on the control side. Data packets transmitted by the control-side transmitter unit include a clock sequence at the beginning, from whose time characteristic it is possible to derive the frequency of a control-side transmitter clock signal underlying the transmission. The receiver unit on the measuring-device side includes a measuring-device-side clock-recognition unit which evaluates the clock sequence and, in order to read in control-side output data included in the data packet, generates a measuring-device-side receiver clock signal, whose frequency corresponds to a great extent to that of the transmitter clock signal on the control side.

FIELD OF THE INVENTION

The present invention relates to a device for serial data transmissionas well as to a method for serial data transmission. Such a device and amethod permit a bidirectional data transmission via a single one-channeldata line.

BACKGROUND INFORMATION

Position-measuring devices which provide an absolute position value arebeing used increasingly in automation technology. Certain disadvantagesof what are termed incremental position-measuring devices are therebyeliminated such as, for example, the necessity of carrying out areference run after switching on in order to find a reference positionwhich is used as reference point for the further position measuring bycounting graduation marks.

Primarily serial data interfaces are used for transmitting the absoluteposition values, since they make do with only a few data-transmissionlines, and nevertheless, have high data-transmission rates. Particularlyadvantageous here are what are called synchronous serial interfaces,which have one unidirectional or bidirectional data line and one clockline. Data packets are transmitted via the data line in synchronism witha clock signal on the clock line.

For example, European Published Patent Application No. 0 171 579describes a synchronous serial data interface having a unidirectionaldata line and a unidirectional clock line. Position values from aposition-measuring device are read out here in synchronism with a clocksignal on the clock line. Among experts, this interface is known by thename “SSI.”

On the other hand, European Published Patent Application No. 0 660 209describes a synchronous serial interface having a bidirectional dataline and a unidirectional clock line. In this case, it is possible totransmit data in both directions—from the sequential electronics to theposition-measuring device and from the position-measuring device to thesequential electronics. The data are transmitted in synchronism with aclock signal on the clock line here, as well. This principle forms thebasis for an interface of the Applicant known under the name “EnDat.”

In the case of both interfaces cited, the data-transmission rate isdetermined by the frequency of the clock signal on the clock line, thatis, a reduction in the frequency of the clock signal reduces thedata-transmission rate and vice versa. In this manner, adaptation toexternal circumstances such as the cable length between sequentialelectronics and the position-measuring device is possible.

An important cost factor in the connection of position-measuring devicesto sequential electronics, e.g., a machine-tool control, is based on thenumber of connecting lines needed, since they substantially determinethe price of the high-quality data cable used. In addition, the numberof connector pins necessary for the plug-in connectors is therebydetermined.

SUMMARY

Example embodiments of the present invention provide a device for serialdata transmission, in which the number of lines necessary for the datatransmission is able to be reduced, and which continues to allowflexible data-transmission rates. A device is provided for serial datatransmission between a position-measuring device and a control unit,made up of an interface unit on the control side and an interface uniton the measuring-device side, which are connected to each other for thetransmission of serial data packets with the aid of a bidirectional datachannel. The interface unit on the control side includes a control-sidetransmitter unit for transmitting serial data packets via the datachannel to a measuring-device-side receiver unit disposed in theinterface unit on the measuring-device side. The interface unit on themeasuring-device side includes a measuring-device-side transmitter unitfor transmitting serial data packets via the data channel to acontrol-side receiver unit disposed in the interface unit on the controlside. Data packets transmitted from the control-side transmitter unitcontain a clock sequence at the beginning, from whose timecharacteristic it is possible to derive the frequency of a control-sidetransmitter clock signal underlying the transmission. The receiver uniton the measuring-device side includes a measuring-device-sideclock-recognition unit which evaluates the clock sequence and, in orderto read in control-side output data contained in the data packet,generates a measuring-device-side receiver clock signal, whose frequencycorresponds to a great extent to that of the control-side transmitterclock signal.

Example embodiments of the present invention provide a method for serialdata transmission with the aid of a device as described herein.

To that end, a method is provided for serial data transmission between aposition-measuring device and a control unit with the aid of a devicemade up of an interface unit on the control side and an interface uniton the measuring-device side, which are connected to each other for thetransmission of serial data packets with the aid of a bidirectional datachannel. The interface unit on the control side includes a control-sidetransmitter unit for transmitting serial data packets via the datachannel to a measuring-device-side receiver unit disposed in theinterface unit on the measuring-device side. The interface unit on themeasuring-device side includes a measuring-device-side transmitter unitfor transmitting serial data packets via the data channel to acontrol-side receiver unit disposed in the interface unit on the controlside. The method includes the follow steps:

-   -   Transmission of control-side output data with the aid of a data        packet from the transmitter unit on the control side via the        data channel to the receiver unit on the measuring-device side        in the time clock of a control-side transmitter clock signal,        the data packet including a clock sequence at the beginning,        from whose time characteristic it is possible to derive the        frequency of the control-side transmitter clock signal,    -   Evaluation of the clock sequence and generation of a        measuring-device-side receiver clock signal, whose frequency        corresponds to a great extent to that of the control-side        transmitter clock signal, in a measuring-device-side        clock-recognition unit which is disposed in the receiver unit on        the measuring-device side,    -   Reading in of control-side output data, contained in the data        packet, as measuring-device-side input data in the time clock of        the receiver clock signal on the measuring-device side.

Further features of example embodiments of the present invention anddetails pertaining thereto are described in the following descriptionwith reference to the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a device according to an exampleembodiment of the present invention for serial data transmission.

FIG. 2 shows a block diagram of a device according to an exampleembodiment of the present invention.

FIG. 3 shows a schematic signal-sequence diagram for the deviceillustrated in FIG. 2.

FIG. 4 shows a signal diagram of a clock sequence.

FIG. 5 shows a counter for evaluating the clock sequence.

DETAILED DESCRIPTION

FIG. 1 shows a block diagram of a device for serial data transmissionbetween a control unit 100 and a position-measuring device 200. For theexchange of data, an interface unit 110 on the control side is disposedin control unit 100, and an interface unit 210 on the measuring-deviceside is disposed in position-measuring device 200, which are connectedto each other via a serial, bidirectional data channel 300. In order totransmit data from control unit 100 to position-measuring device 200, acontrol-side transmitter unit 120 is disposed in interface unit 110 onthe control side, and a measuring-device-side receiver unit 230 isdisposed in interface unit 210 on the measuring-device side. Analogousthereto, data are transmitted in the reverse direction via a transmitterunit 220 on the measuring-device side and a receiver unit 130 on thecontrol side.

The power supply may be fed to position-measuring device 200 via supplylines VCC, GND by control unit 100.

A data channel 300 is provided for the transmission of data betweenposition-measuring device 200 and control unit 100. Data channel 300 isone-channel, that is, in the simplest case, the transmission may takeplace via a single line on which the logic values of the individual bitsof the data packets are transmitted in the form of voltage levelsrelative to reference potential GND. Advantageously, however, datachannel 300 is arranged differentially, i.e., the data are transmittedvia a line pair 310, the signals to be transmitted being transmittedinverted relative to each other via the two lines. To that end, onedifferential driver unit 320, 330 and one differential receiver unit340, 350 each are disposed on the control side and on themeasuring-device side. The outputs of driver units 320, 330 and theinputs of receiver units 340, 350 are connected correspondingly to linepair 310. Differential data transmission is conventional and is notfurther explained.

Since the transmission of data via data channel 300 takes place in bothdirections over only one line pair 310, in order to avoid datacollisions, only one of driver units 320, 330 may ever be switched toactive. Driver units 320, 330 are activated by enable signals CU_EN,EC_EN, which are controlled by assigned transmitter units 120, 220. Forexample, for the transmission of data from control unit 100 toposition-measuring device 200, driver unit 320 on the control side isswitched to active by control-side enable signal CU_EN, and driver unit330 on the measuring-device side is switched to passive bymeasuring-device-side enable signal EC_EN. Since in the case of theconfiguration described here, data transmission from position-measuringdevice 200 to control unit 100 is always initiated by control unit 100,this setting of enable signals EC_EN, CU_EN is particularly advantageousas the basic setting.

A processing unit 150 feeds control-side output data CU_DO tocontrol-side transmitter unit 120, which forms data packets andtransmits them as a serial data stream via data channel 300 toposition-measuring device 200. To store control-side output data CU_DOtemporarily, an output-data memory 170 is provided in control-sidetransmitter unit 120. The data-transmission rate, thus the speed withwhich the data packets are transmitted bit-by-bit, is determined by acontrol-side transmitter clock signal CU_TXC generated in a clockgenerator 160 that likewise is disposed in interface unit 110 on thecontrol side.

In order to read in a data packet, receiver unit 230 on themeasuring-device side needs a measuring-device-side receiver clocksignal EC_RXC that runs synchronously with the arriving serial datastream, at least for the duration of the transmission of the datapacket. In order to be able to generate it, at the beginning of the datapacket, transmitter unit 120 on the control side transmits a clocksequence TS, e.g., the bit sequence 1-0-1, from whose timecharacteristic, measuring-device-side receiver clock signal EC_RXC isderived in a clock-recognition unit 240 disposed in receiver unit 230 onthe measuring-device side. For example, this may be accomplished bymeasuring edge spacings of clock sequence TS.

After measuring-device-side receiver clock signal EC_RXC is available,the data contained in the data stream may be extracted and passed on asmeasuring-device-side input data EC_DI for further processing to aposition-measuring unit 250 included in position-measuring device 200.Depending on the link of receiver unit 230 on the measuring-device sideto position-measuring unit 250, input data EC_DI may be storedtemporarily in an input-data memory 280 before being passed on. Thepresence of input data EC_DI in input-data memory 280 is then signaledto position-measuring unit 250, for example, via a signal line 295 frominput-data memory 280. Alternatively, the signaling may also beperformed by clock-recognition unit 240.

Data packets, which are transmitted in this manner from control unit 100to position-measuring device 200, may include any information asdesired:

-   -   Instructions, e.g., for requesting position values or memory        contents (“electronic type label”)    -   Addressing information for the specific selection of one        position-measuring device 200 (necessary if a plurality of        position-measuring devices 200 are connected to one control unit        100)    -   Control or configuration data, e.g., calibration values

For the data transmission in the opposite direction, thus, fromposition-measuring device 200 to control unit 100, position-measuringunit 250 feeds measuring-device-side output data EC_DO to transmitterunit 220 on the measuring-device side. An output-data memory 270 may beprovided for temporary storage here, as well. For example,measuring-device-side output data EC_DO may be position data or memorycontents requested by instruction of control unit 100. Transmitter unit220 on the measuring-device side in turn forms data packets, which ittransmits with a data-transmission rate that is determined by ameasuring-device-side transmitter clock signal EC_TXC, in the form of aserial data stream via data channel 300 to receiver unit 130 on thecontrol side. The beginning of the transmission, in this case synonymouswith the start of measuring-device-side transmitter clock signal EC_TXC,may again be initiated via a signal line 290 by output-data memory 270on the measuring-device side.

The data-word length of the data to be transmitted is predefined tointerface units 110, 210 by parameters n that may either be setpermanently, or else may be programmable. This information is needed,inter alia, for the correct control of enable signals CU_EN, EC_EN, aswell. Furthermore, in each case, operating clock signals CLK areavailable to interface units 110, 210 for the control of internalsequences. For instance, they may be used by clock generators 160, 260for generating transmitter clock signals CU_TXC, EC_TXC, and possibly inclock-recognition units 140, 240 for ascertaining receiver clock signalsCU_RXC, EC_RXC.

In the simplest case, transmitter clock signal EC_TXC on themeasuring-device side may be receiver clock signal EC_RXC on themeasuring-device side. Moreover, if it can be ensured that thetransmission of the data stream in the direction of control unit 100proceeds largely in synchronism with the data stream received fromcontrol unit 100, then transmission of a clock sequence TS may possiblybe omitted in this data direction, since control-side transmitter clocksignal CU_TXC may be used as control-side receiver clock signal CU_RXCon the side of control unit 100 for the reception of the data stream.

However, in view of increased transmission reliability, it isparticularly advantageous if data packets transmitted fromposition-measuring device 200 to control unit 100 likewise include aclock sequence TS, e.g., bit sequence 0-1-0, at the beginning, fromwhich control-side receiver clock signal CU_RXC for the reception of thearriving data stream is derived in a control-side clock-recognition unit140 disposed in receiver unit 130 on the control side. In this case,measuring-device-side transmitter clock signal EC_TXC is generated in aclock generator 260. This design approach has the further advantage thatdifferent data-transmission rates may be used in each data direction.With the aid of control-side receiver clock signal CU_RXC, receiver unit130 on the control side extracts the data contained in the arrivingserial data stream, stores it in an input-data memory 180 on the controlside, and passes it on in the form of control-side input data CU_DI toprocessing unit 150.

Both memory modules writable in parallel and serially writable memorymodules may be used as input-data memories 180, 280 and output-datamemories 170, 270, respectively. Memory modules writable in parallel arealso known as input or output registers. Serially writable memorymodules are shift registers, for example, or special serial memories,particularly with first-in/first-out architecture.

In principle, it is possible that processing unit 150, orposition-measuring unit 250, already inserts a clock sequence TS intooutput data CU_DO, EC_DO. However, in the case of already existingprocessing units 150 and position-measuring units 250, this requires amodification of the interface used to transmit output data CU_DO, EC_DO.On the other hand, if the insertion of clock sequence TS is carried outin transmitter unit 120, 220, then, if appropriate, already existingprocessing units 150, as well as position-measuring units 250, maycontinue to be used without modifications. This holds true especially ifoutput data CU_DO, EC_DO are fed via synchronous serial interfaces, asshown below in FIG. 2.

FIG. 2 shows a block diagram of a device according to an exampleembodiment of the present invention. In this exemplary embodiment,processing unit 150 is connected to interface unit 110 on the controlside, and position-measuring unit 250 is connected to interface unit 210on the measuring-device side, by synchronous serial interfaces.

For control unit 100, this means that control-side output data CU_DO arewritten by processing unit 150 into control-side output-data memory 170serially and in synchronism with a processing clock CU_CLK. In the samemanner, control-side input data CU_DI are transmitted from input-datamemory 180 on the control side to processing unit 150 serially and insynchronism with processing clock CU_CLK.

Interfaces of this type are described, e.g., in European PublishedPatent Application No. 0 660 209, for transmitting data via atwo-channel data channel with separate transmission of clock pulse anddata.

Advantageously, control-side output-data memory 170 and input-datamemory 180, respectively, are serial memory modules havingfirst-in/first-out (FIFO) architecture. This means that data bits areread out from the memory in the same order in which they are writteninto the memory. In this manner, the writing of data into data memories170, 180 is decoupled from the reading of data out of data memories 170,180.

The arrival of control-side output data CU_DO is signaled tocontrol-side clock generator 160 via a signal line 190, e.g., fromcontrol-side output-data memory 170. Thereupon, it starts control-sidetransmitter clock signal CU_TXC, and first of all transmits clocksequence TS, and subsequently (represented symbolically by a changeoverswitch) control-side output data CU_DO from the FIFO as a serial datastream to position-measuring device 200. Thus, in this case, thetransmitted data packet is made up merely of clock sequence TS andcontrol-side output data CU_DO. By using a FIFO, the data packet istransmitted still during the transfer of output data CU_DO intooutput-data memory 170 on the control side. The frequency ofcontrol-side transmitter clock signal CU_TXC is less than or equal tothe frequency of processing clock CU_CLK. This ensures that data bitsare not extracted from output-data memory 170 on the control side fasterthan they are fed to it.

In position-measuring device 200, measuring-device-sideclock-recognition unit 240 ascertains the transmission data rate fromclock sequence TS transmitted at the beginning of the arriving datastream, and generates measuring-device-side receiver clock signalEC_RXC. After clock sequence TS has been received completely,clock-recognition unit 240 switches measuring-device-side receiver clocksignal EC_RXC (as measuring-device clock EC_CLK), as well as theremainder of the arriving data packet, which really corresponds tomeasuring-device-side input data EC_DI, through to position-measuringunit 250. It is possible to dispense with an input-data memory 280 onthe measuring-device side if position-measuring unit 250 is able toprocess measuring-device-side input data EC_DI directly in thedata-transmission speed used. If this is not the case, an input-datamemory 280 (not shown) may be used on the measuring-device side, e.g.,in the form of a serial FIFO, here, as well.

If data, e.g., position values or memory contents, are requested ofposition-measuring unit 250 with the arriving data packet, transmitterunit 120 on the control side switches control-side driver unit 320 topassive by control-side enable signal CU_EN, while transmitter unit 220on the measuring-device side switches measuring-device-side driver unit330 to active by measuring-device-side enable signal EC_EN. Transmitterunit 220 on the measuring-device side subsequently transmits a clocksequence TS to begin with to control unit 100, and then switches throughmeasuring-device-side output data EC_DO directly onto data channel 300.Measuring-device-side transmitter clock signal EC_TXC is likewisegenerated in measuring-device-side clock-recognition unit 240, and inthis exemplary embodiment, has the frequency of measuring-device clockEC_CLK, as well.

In the event the requested data are not immediately available, the datapacket thus generated contains an empty area, e.g., made up of acontinuous sequence of identical bits, between clock sequence TS and thedata actually requested. In order to indicate the beginning of therequested data word to processing unit 150 in control unit 100, aninverse bit may be used, which brings about a change in the logic levelof the incoming data stream.

In receiver unit 130 on the control side, the incoming data stream isfed to control-side clock-recognition unit 140 which, for example, bymeasuring edge spacings, generates from clock sequence TS a control-sidereceiver clock signal CU_RXC that corresponds to measuring-device-sidetransmitter clock signal EC_TXC. With the aid of this clock signal, thebits transmitted with the data stream are written into input-data memory180 on the control side. The contents of input-data memory 180 on thecontrol side are able to be read out continuously by processing unit 150with processing clock CU_CLK, since the actual beginning of thetransmission of the requested data is identified clearly by the inversebit. In this data direction, as well, it is necessary to prevent thecontents of input-data memory 180 on the control side from being readout faster than written. For this reason, the frequency ofmeasuring-device-side transmitter clock signal EC_TXC, which determinesthe data-transmission rate of the incoming data stream, must be greaterthan or equal to processing clock CU_CLK.

In order to be able to compensate for deviations, caused by componenttolerances and/or external influences (e.g., temperature fluctuations),in the frequency of clock signals CU_TXC, CU_RXC, EC_TXC, EC_RXCnecessary for the data transmission, it may be provided to select forthe data transmission from control unit 100 to position-measuring device200, a lower, and for the data transmission from position-measuringdevice 200 to control unit 100, a higher frequency than the frequency ofprocessing clock CU_CLK. Thus, for example, the frequency ofcontrol-side transmitter clock signal CU_TXC, and ofmeasuring-device-side receiver clock signal EC_RXC corresponding to it,amounts to 0.75 to 0.9 times the frequency of processing clock CU_CLK,and the frequency of measuring-device-side transmitter clock signalEC_TXC and of control-side receiver clock signal CU_RXC amounts to 1.05to 1.20 times the frequency of processing clock CU_CLK. For the exampleabove, it follows from this that, depending on the data direction,clock-recognition unit 240 on the measuring-device side switchesmeasuring-device-side receiver clock signal EC_RXC ormeasuring-device-side transmitter clock signal EC_TXC asmeasuring-device clock EC_CLK to position-measuring unit 250.

FIG. 3 shows a schematic signal-sequence diagram for the deviceillustrated in FIG. 2. Shown here is a typical communication cyclebetween control unit 100 and position-measuring device 200, in whichfirst an instruction word BW, e.g., a request instruction for a positionvalue, is transmitted from control unit 100 to the position-measuringdevice, whereupon the position-measuring device transmits the requesteddata word, e.g., position value POS, to the control unit.

The communication cycle begins with the synchronous serial transmissionof control-side output data CU_DO, thus, in this case, instruction wordBW, into output-data memory 170 on the control side. In this example,instruction word BW is made up of four instruction bits X. Thesynchronization of the transmission is accomplished with processingclock CU_CLK. Thereupon, clock generator 160 on the control sidegenerates control-side transmitter clock signal CU_TXC, and transmitterunit 120 on the control side transmits a data packet made up of clocksequence TS, here the bit sequence 1-0-1, followed by instruction wordBW as serial data stream MOUT via data channel 300 to position-measuringdevice 200. In simple systems in which the only instruction is a requestfor position data, it is also possible to dispense with instruction wordBW (data-word length=0). In this special case, the transmission of clocksequence TS is already interpreted as request for position data.

In position-measuring device 200, clock-recognition unit 240 on themeasuring-device side generates measuring-device-side receiver clocksignal EC_RXC from clock sequence TS. Since no output-data memory 270 isprovided on the measuring-device side, received instruction word BW ispassed on in serial form directly to position-measuring unit 250.Measuring-device-side receiver clock signal EC_RXC, which is fed asmeasuring-device clock EC_CLK to position-measuring unit 250, is usedfor the synchronization.

Regardless of how long position-measuring unit 250 needs in order toprovide the requested data, immediately after receipt of instructionword BW, transmitter unit 220 on the measuring-device side transmits aserial data stream SOUT, beginning with clock sequence TS (here, 0-1-0),followed by a constant value, in this example a logic “0”, to controlunit 100. The transmission takes place synchronously withmeasuring-device-side transmitter clock signal EC_TXC, that likewise isgenerated by clock-recognition unit 240 on the measuring-device side. Ifthe requested data, e.g., ascertained position value POS, is ready, itstransmission is initiated with an inverse bit, in this case, a logic“1”. For reasons of clarity, position value POS here is made up of onlyeight position bits Y. In practice, actual position values POS are madeup of 24-40 bits, for example.

From clock sequence TS transmitted with the arriving data stream,clock-recognition unit 140 on the control side generates control-sidereceiver clock signal CU_RXC. Receiver unit 130 on the control side usesit to write the bits following clock sequence TS into input-data memory180 on the control side. Finally, control-side input data CU_DI (made upof constant value “0”, followed by inverse bit “1” and position valuePOS) are transmitted in synchronism with processing clock CU_CLK toprocessing unit 150. The communication cycle is thus ended.

Naturally, more complex communication cycles in which more than one dataword is transmitted in one data direction may also be realized using adevice as described herein. In this case, it is especially advantageousif, per communication cycle, a clock sequence TS is transmitted onlybefore the first data word transmitted in a data direction, andtransmitter clock signal CU_TXC, EC_TXC or receiver clock signal EC_RXC,CU_RXC associated with it is then retained for further data words in therespective data direction.

The ascertainment of receiver clock signal EC_RXC, CU_RXC from a clocksequence TS shall now be described with reference to FIGS. 4 and 5. FIG.4 shows a signal diagram of a clock sequence TS, which here is made upof the bit sequence 1-0-1. In this example, the signal level prior toarrival of clock sequence TS corresponds to a logic “0”. The period oftime which one bit of clock sequence TS, and therefore also thefollowing bits of the data stream, requires, is determined by twodifferent successive signal edges, for example, in the case of a logic“1”, by one rising signal edge followed by one falling signal edge, andcorresponds to period duration T of receiver clock signal EC_RXC, CU_RXCto be ascertained.

As FIG. 5 shows, in order to measure period duration T, a counter 400may be used, with which the period of time between two signal edges ismeasurable. Thus, in order to measure period duration T in the case of alogic “1”, counter 400 is started with a rising signal edge and stoppedagain with a falling signal edge. Between the signal edges, counter 400counts with the frequency of a counting pulse ZCLK. For example,respective operating clock CLK may be used as counting pulse ZCLK. Afterthe measurement has been performed, counter value SUM is output, andcounter 400 may be reset again via a reset signal RES for the nextmeasurement. Period duration T may now be calculated with the aid ofcounter value SUM and counting pulse ZCLK.

In this context, the frequency of counting pulse ZCLK is to be selectedsuch that the error resulting from the quantization is so small thateach bit transmitted in the corresponding data direction in onecommunication cycle may be reliably sampled and recorded. For thetransmission of data packets having up to 140 bits, it may be providedto select 6 to 8 times the highest frequency to be expected as countingfrequency ZCLK for ascertaining receiver clock signal EC_RXC, CU_RXC.

Different, especially longer bit sequences may, of course, also be usedas clock sequence TS, from whose edge spacings it is possible to derivereceiver clock signal EC_RXC, CU_RXC to be ascertained. Likewise, aplurality of counters 400 may also be used in order to evaluatedifferent edge spacings of the clock sequence, and thus to design theascertainment of receiver clock signal EC_RXC, CU_RXC to be redundant,or to permit averaging.

Since interface units 110, 210 are purely digital circuits, they areparticularly well suited for implementation in programmable logicmodules (e.g., FPGA) or application-specific integrated circuits(ASICs). Moreover, there is the possibility of using microcontrollersfor their implementation.

1-19. (canceled)
 20. A device for serial data transmission between acontrol unit and a position-measuring device, comprising an interfaceunit on a control side and an interface unit on a measuring-device side,the interface units being connected to each other for transmission ofserial data packets by a bidirectional data channel; a control-sidetransmitter unit, arranged in the interface unit on the control side,adapted to transmit serial data packets via the data channel to ameasuring-device-side receiver unit arranged in the interface unit onthe measuring-device side; a measuring-device-side transmitter unit,arranged in the interface unit on the measuring-device side, adapted totransmit serial data packets by the data channel to a control-sidereceiver unit arranged in the interface unit on the control side;wherein the control-side transmitter unit is adapted to transmit datapackets that include a clock sequence at a beginning, a frequency of acontrol-side transmitter clock signal underlying the transmission beingderivable from a time characteristic of the clock sequence; and whereinthe receiver unit on the measuring-device side includes ameasuring-device-side clock-recognition unit adapted to evaluate theclock sequence and, in order to read in control-side output dataincluded in the data packet, to generate a measuring-device-sidereceiver clock signal having a frequency that substantially correspondsto the frequency of the control-side transmitter clock signal.
 21. Thedevice according to claim 20, wherein the clock-recognition unit on themeasuring-device side is adapted to feed the measuring-device-sidereceiver clock signal as a measuring-device-side transmitter clocksignal to the transmitter unit on the measuring-device side.
 22. Thedevice according to claim 20, wherein the transmitter unit on themeasuring-device side is adapted to transmit data packets including aclock sequence at a beginning, a frequency of a measuring-device-sidetransmitter clock signal underlying the transmission being derivablefrom a time characteristic of the clock sequence; and wherein thereceiver unit on the control side includes a control-sideclock-recognition unit adapted to evaluate the clock sequence and, inorder to read in measuring-device-side output data included in the datapacket, to generate a control-side receiver clock signal having afrequency that substantially corresponds to the frequency of themeasuring-device-side transmitter clock signal.
 23. The device accordingto claim 20, wherein the control unit includes a processing unit adaptedto feed control-side output data to be transmitted to the control-sidetransmitter unit, the device further comprising a synchronous serialinterface adapted to transmit control-side input data received from thecontrol-side receiver unit to the processing unit.
 24. The deviceaccording to claim 20, wherein at least one of (a) the transmitter uniton the control side includes a control-side output-data memory adaptedto store control-side output data to be transmitted and (b) the receiverunit on the control side includes a control-side input-data memoryadapted to store received control-side input data.
 25. The deviceaccording to claim 24, wherein at least one of (a) the output-datamemory on the control side and (b) the input-data memory on the controlside includes a serial memory having first-in/first-out architecture.26. The device according to claim 20, wherein the position-measuringdevice includes a position-measuring unit, the receiver unit on themeasuring-device side adapted to transmit received measuring-device-sideinput data to the position-measuring unit, the position-measuring unitadapted to feed measuring-device-side output data to be transmitted tothe transmitter unit on the measuring-device side by a synchronousserial interface.
 27. The device according to claim 20, wherein at leastone of (a) the transmitter unit on the measuring-device side includes ameasuring-device-side output-data memory adapted to storemeasuring-device-side output data to be transmitted and (b) the receiverunit on the measuring-device side includes a measuring-device-sideinput-data memory adapted to store received measuring-device-side inputdata.
 28. The device according to claim 27, wherein at least one of (a)the output-data memory on the measuring-device side and (b) theinput-data memory on the measuring-device side includes a serial memoryhaving first-in/first-out architecture.
 29. A method for serial datatransmission between a position-measuring device and a control unit,including a device having: an interface unit on a control side and aninterface unit on a measuring-device side, the control units connectedto each other for transmission of serial data packets by a bidirectionaldata channel; a control-side transmitter unit, arranged in the interfaceunit on the control side, adapted to transmit serial data packets by thedata channel to a measuring-device-side receiver unit arranged in theinterface unit on the measuring-device side; and a measuring-device-sidetransmitter unit, arranged in the interface unit on the measuring-deviceside, adapted to transmit serial data packets by the data channel to acontrol-side receiver unit arranged in the interface unit on the controlside, comprising: transmitting control-side output data by a data packetby the transmitter unit on the control side via the data channel to thereceiver unit on the measuring-device side in accordance with a timeclock of a control-side transmitter clock signal, the data packetincluding a clock sequence at a beginning, a frequency of thecontrol-side transmitter clock signal derivable from a timecharacteristic of the clock sequence; evaluating the clock sequence andgenerating a measuring-device-side receiver clock signal having afrequency that substantially corresponds to the frequency of thecontrol-side transmitter clock signal, in a measuring-device-sideclock-recognition unit arranged in the receiver unit on themeasuring-device side; reading in of control-side output data, includedin the data packet, as measuring-device-side input data in the timeclock of the receiver clock signal on the measuring-device side.
 30. Themethod according to claim 29, wherein the data packet, including theclock sequence and the control-side output data fed to the transmitterunit on the control side by a processing unit included in the controlunit, is formed in the control-side transmitter unit.
 31. The methodaccording to claim 29, further comprising transmitting themeasuring-device-side input data to a position-measuring unit arrangedin the position-measuring device.
 32. The method according to claim 31,further comprising feeding data, by the position-measuring unit,requested by an instruction included in the measuring-device-side inputdata, as measuring-device-side output data to the transmitter unit onthe measuring-device side.
 33. The method according to claim 32, furthercomprising: transmitting the measuring-device-side output data by a datapacket by the transmitter unit on the measuring-device side via the datachannel to the receiver unit on the control side in a time clock of ameasuring-device-side transmitter clock signal, the data packetincluding a clock sequence at a beginning, a frequency of themeasuring-device-side transmitter clock signal derivable from a timecharacteristic of the clock sequence; evaluating the clock sequence andgenerating a control-side receiver clock signal having a frequency thatsubstantially corresponds to a frequency of the measuring-device-sidetransmitter clock signal, in a control-side clock-recognition unitarranged in the receiver unit on the control side; and reading in of themeasuring-device-side output data, included in the data packet, ascontrol-side input data in the time clock of the receiver clock signalon the control side.
 34. The method according to claim 33, wherein thedata packet is formed in the transmitter unit on the measuring-deviceside from the clock sequence and the measuring-device-side output data.35. The method according to claim 33, further comprising transmittingthe control-side input data to a processing unit included in the controlunit.
 36. The method according to claim 29, further comprising at leastone of (a) temporarily storing the control-side output data in acontrol-side output-data memory arranged in the transmitter unit on thecontrol side and (b) temporarily storing the control-side input data ina control-side input-data memory arranged in the receiver unit on thecontrol side.
 37. The method according to claim 29, further comprisingat least one of (a) temporarily storing the measuring-device-side inputdata in a measuring-device-side input-data memory arranged in thereceiver unit on the measuring-device side and (b) temporarily storingthe measuring-device-side output data in a measuring-device-sideoutput-data memory arranged in the transmitter unit on themeasuring-device side.
 38. The method according to claim 29, furthercomprising evaluating the clock sequence by measuring edge spacings.